1. Field of the Invention
This invention relates to a coating machine with counter-flow and parallel-flow air conduction for coating tablets, granules, pellets, dragees and the like with one or more coating compositions, of the type wherein the cores to be coated are arranged in a rotatably driven, perforated drum mounted on a housing which comprises an air conducting channel surrounding the drum at its outer periphery, which air channel is provided with air from an air supply fixed to a housing, with air streams differently directed into the drum, the drum further comprising a pivot bearing which is constructed as a hollow shaft and through which an additional axial air stream can be conducted out of the drum.
2. Description of the Prior Art
A coating machine of the aforementioned type is known in which counter-flow and parallel-flow air conduction takes place via an air distributor, which is rigidly installed in the housing on the rear side of the rotatable drum and in which air distribution for the purpose of counter-flow or parallel-flow conduction takes place by the switching of valves in the air distributor. Air conduction here takes place in a closed system without loss of air, and it is possible to switch from a parallel-flow drying process to a counter-flow one. In addition, extraction of air from the interior of the drum through the hollow shaft of the drum is known. For control of air conduction in the known coating machine, a total of at least three air valves are required, each of which must be driven accordingly. As a result, however, there arises the disadvantage of a relatively costly air distributor, and furthermore operational reliability in driving the valves cannot always be guaranteed, because there is no clear indication as to whether the valve has in actual fact been switched in the desired manner or not. Moreover, the air distributor itself and the air conducting channels of the housing and drum covered by the air distributor can be cleaned only with difficulty.